Repairs – Page 102 – The Smell of Molten Projects in the Morning

Storm Door Brace: Now, With Inserts!

The mid-1950s wood doors on our house have wood storm doors with interchangeable wood-framed glass and screen panels. Twice a year, the diligent homeowner will swap the panels to match the season; during the last 60+ years, the glass panels remain undropped.

The back door has a diagonal tension brace to hold the door in shape; the door may be slightly distorted or the frame slightly out of square. In any event, the brace obstructs the panel, so the semiannual ritual includes loosening the brace and removing four screws. During the last 60+ years, the screw holes have required repair / filling several times; about five years ago, I plugged them with epoxy putty and drilled them to fit the screws.

That repair having aged out, I was about to renew the epoxy when I realized that I now have brass inserts that would work even better, if I replaced the original wood screws with 10-32 machine screws.

I cut the screws to the exact length using the brace and brass insert as a fixture:

Storm door - screw cutting — Storm door – screw cutting

The vacuum cleaner nozzle to the lower right inhales the debris from the Dremel cutoff wheel that would otherwise fill the shop; I used up the last half of a wheel on four stainless steel screws.

Because each end of the brace has two screws, I knew that I couldn’t just drill out the four holes, plant four inserts, and be done with the job: the first insert on each end could go pretty nearly anywhere, but the second insert must match the brace hole spacing. The only way I know how to do that is to epoxy the first two inserts in place and let them cure, drill the other two holes slightly oversize, mount those inserts on the brace, butter them with epoxy, put the brace in place, tighten the first two screws, snug the brace, and hope I didn’t epoxy the brace to the door or the screws to the inserts.

Slips of waxed paper between the brace and the door prevented the first problem and oiling the screws prevented the second. It’s not the best-looking job I’ve ever done, but nobody will ever see the inserts behind the brace:

Storm door - inserts — Storm door – inserts

Now, we’re ready for winter and I’m ready for spring!

Most likely, the new owners (whoever and whenever they may be) will never use these inserts, as they’ll replace all the windows & doors, plus sand & refinish the hardwood floors, before moving in …

2016-11-05

Cast Iron Pan Electrolysis: Anode Fragment

Sacrificing a scrap EMI shield from a junked PC as the electrolysis anode, I grabbed a tab with the battery charger clamp:

Cast iron pan electrolysis - bucket — Cast iron pan electrolysis – bucket

Turns out it didn’t survive the encounter:

Cast iron pan electrolysis - anode front — Cast iron pan electrolysis – anode front

That white blob extends around to the other side:

Cast iron pan electrolysis - anode rear — Cast iron pan electrolysis – anode rear

Yeah, it got hot enough to melt a blob from the 6 gallon plastic bucket before burning through.

I tossed that into the garage so I wouldn’t forget it aaaand here we are …

2016-10-27

Hand Sprayer Hose Kink Prevention

Mary’s new half-gallon sprayer arrived with a kink in the hose just below the handle, which is about what you’d expect from a non-reinforced plastic tube jammed into the smallest possible box containing both the sprayer and its wand. Fortunately, the Box o’ Springs had one that just fit the hose and jammed firmly into the handle:

The kink slowly worked its way out after being surrounded by the spring and shouldn’t come back.

That was easy…

2016-10-26

American Standard Kitchen Faucet: Ceramic Valve

It seems everybody must disassemble an American Standard kitchen faucet to replace the spout seal O-rings, as my description of How It’s Done has remained in the top five most popular posts since I wrote it up in 2009.

About two years ago, I replaced the valve cartridge with a (presumably) Genuine Replacement; unlike the O-rings, the original valve lasted for nigh onto a decade. A few weeks ago, the replacement valve began squeaking and dribbling: nothing lasts any more. Another (presumably) Genuine Replacement, this time from Amazon, seems visually identical to the previous one and we’ll see how long it lasts.

I always wondered what was inside those faucets and, after breaking off the latching tabs in the big housing to the upper right, now I know:

American Standard Faucet - disassembled — American Standard Faucet – disassembled

You get a bunch of stuff for twelve bucks! The stainless steel valve actuator is off to the right, still grabbed in the bench vise.

The valve action comes from those two intricate ceramic blocks with a watertight sliding fit:

American Standard Faucet - ceramic valve parts — American Standard Faucet – ceramic valve parts

In fact, you (well, I) can wring the slabs together, just like a pair of gauge blocks. That kind of ultra-smooth surface must be useful for some other purpose, even though I can’t imagine what it might be…

2016-10-24

Kindle Fire Power Switch Rebuild

The single moving part on my first-generation (2011) Kindle Fire tablet stopped working: the power switch became erratic, to the point where the only dependable way to turn the thing on required the USB charging cable. Obviously not a long-term solution.

Having nothing to lose, I consulted the Internet’s vast steaming pile of advice on how to pop the Kindle’s cover, picked one, and ran with it. Basically, you jam a sharp tool into the end with the speakers, then crack the back off along both sides, leading to this:

Kindle Fire - pre-teardown overview — Kindle Fire – pre-teardown overview

Things to note:

No need to remove the battery: pull the heavy connector straight out
Disconnect the battery first, before unplugging anything else
Most of the ribbon cable connectors have a white flip-up latch
You will break the ground shield from the flex PCB to the battery along the left edge
The antenna must make that 270° turn into the minuscule U.FL connector
The four-wire cable to the speakers has a pull-out connector in the lower right corner
The PCB backplate on the large video (?) connector in the upper right pulls straight up-and-out

Remove the six obvious screws, pull the battery edge of the board upward, and rotate the whole affair out of the chassis:

Kindle Fire - power LED board - in place — Kindle Fire – power LED board – in place

Protip: the power switch is not mounted on the tiny PCB (under the ribbon cable with the blue tab) sometimes advertised as the Power Button Board. That tiny PCB suspends an amber/green LED behind the visible button, but a yoke surrounds the LED to transfer the button motion to the power switch soldered to the CPU board. Replacing that board will not cure an erratic power switch; I think the entire CPU board is the FRU.

Fortunately, I can actually see the power switch and know sorta-kinda what to expect.

A bit of awkward multimeter probing showed the switch was defunct, with intermittent action and generally high resistance when pressed. I unsoldered the switch, verified that it didn’t work in isolation, and examined some likely candidates from the Big Box o’ Small Switches:

Kindle Fire - potential power switches — Kindle Fire – potential power switches

Some could be made to fit and maybe actually function, with effort ranging from tedious to Really Hard.

Then it occurred to me that maybe, just maybe, I could refurbish / clean / repair the Kindle’s switch contacts. Shaving off the two heat-staked plastic bumps on the front and prying the side latches outward produced an explosion of small parts:

Kindle Fire - disassembled power switch — Kindle Fire – disassembled power switch

That’s after cleaning the expected grunge from the three contact strips in the body and the innermost of the two (!) buckling-spring contact doodads (bottom left). I scrubbed with the cardboard-ish stem of a cotton swab and, as always, a dot of DeoxIT Red, inserted the unused-and-pristine contact spring doodad (bottom right) first, and reassembled the switch in reverse order.

The metal shell around the body has two locating tabs that fit in two PCB holes, giving the switch positive alignment and good strain relief. The front view shows the three human-scale components amid a sea of 0201 SMD parts:

Kindle Fire - repaired power switch - front — Kindle Fire – repaired power switch – front

For completeness, the view from the battery side:

Kindle Fire - repaired power switch - rear — Kindle Fire – repaired power switch – rear

It’s worth noting that you can see right through the 3.5 mm headphone jack, which accounts for the remarkable amount of dust & fuzz I blew out of the chassis. The overall dust sealing isn’t great, but after five years of life in my pocket, I suppose that’s to be expected.

Installing the board requires holding all the cables out of the way (tape the antenna & speaker wires to the battery), aiming the USB connector into its cutout, rotating the battery edge of the board downward, pushing the mesh EMI shield along the battery upward to clear the board edge, not forcing anything, and eventually it slides into place.

Insert cables, latch latches, plug in the battery, snap the rear cover in place, and It Just Works again. The power switch responds to a light touch with complete reliability; it hasn’t worked this well in a year.

Bonus: To my utter & complete astonishment, disconnecting the battery for few hours had no effect on the stored data: it powered up just fine with all the usual settings in place. I expected most of the settings to live in the Flash file system, but apparently nothing permanent lives in RAM.

Take that, entropy!

2016-10-14

More Cheap eBay Hardware Failures

Data points…

Another knockoff Neopixel failed in the usual way, after a few days of operation: the first W2812B chip in the string gave off intermittent and random flashes of pure primary colors, the second was dead in the water. Replacing the first chip with Yet Another Knockoff from the same lot restored the tube to good health.

Some oscilloscope probing revealed a pooched serial data output with no active pullup, so the output data rarely exceeded VCC/2 and generally wouldn’t be accepted by the downstream W2812B. Nothing to show for it, as I couldn’t be bothered to upload a scope shot. Maybe next time.

One of the counterfeit FTDI USB-to-serial adapters in another tube base failed after a few weeks of operation, with symptoms ranging from hangs while downloading the Arduino program to readback verify mismatches. Replacing the failed adapter and the knockoff Arduino Pro Mini with a knockoff Arduino Nano (using a CH340 USB interface, presumably not a counterfeit) from a recently arrived envelope restored that tube to good health.

All in all, those knockoff Neopixels have been a constant source of amusement; worth every penny just for the privilege of holding them up for ridicule. The “genuine” FTDI chips weren’t much of a surprise, but I am mildly surprised they work so poorly.

2016-10-07

Miniblind Bottom Rail Caps

A few days after installing the replacement cord caps, I bumped the bottom rail of the miniblind while opening the window and had one endcap disintegrate; apparently window hardware isn’t hardened against prolonged UV exposure. Who knew?

Fortunately, I can fix that:

Making the walls three threads wide provides enough room for a single solid infill thread:

Miniblind Endcaps - Slic3r Preview — Miniblind Endcaps – Slic3r Preview

The exterior shape comes from a hull wrapped around six circles: four to define the corner radius and a pair that bump the center out by the calculated chord height. The interior shape comes from a pair of chord-radius polygonal circles (they only have three facets across the length of the inside wall) that fit the bottom rail almost perfectly.

As always, natural PETG has a crystalline, slightly transparent, appearance:

I should spring for some opaque white filament, but that way lies madness; I might start caring what these things look like.

You can buy entire miniblinds for a few bucks a pop, but the last time we did that, they were different than the ones we had before. That wouldn’t matter if the standard miniblind mounting brackets fit our 1955 Anderson windows, but noooo they don’t: the custom adapters I machined for the first miniblind brackets, of course, didn’t fit the new miniblinds.

Now I can just snap the replacement endcaps (and cord pulls) in place, declare victory, and move on.

The OpenSCAD source code as a GitHub Gist:

	// Cap for miniblind cord and bottom rail endcaps
	// Ed Nisley KE4ZNU – September 2016

	Layout = "BaseEndCap"; // CordCap BaseEndCap

	//- Extrusion parameters – must match reality!

	ThreadThick = 0.25;
	ThreadWidth = 0.40;

	Protrusion = 0.1;

	HoleWindage = 0.2;

	//——
	// Dimensions

	OD1 = 0;
	OD2 = 1;
	LENGTH = 2;

	//———————-
	//- Build it

	if (Layout == "CordCap") {

	Cap = [9.0,16.0,25.0];
	Cord = [2.5,7.0,Cap[LENGTH] – 5];
	NumSides = 8;

	difference() {

	hull() { // overall shape
	translate([0,0,Cap[LENGTH] – Cap[OD1]/2])
	sphere(d=Cap[OD1],$fn=NumSides);
	translate([0,0,0.5*Cap[OD2]/2])
	sphere(d=Cap[OD2],$fn=2*NumSides); // round the bottom just a bit
	}

	translate([0,0,-Cap[LENGTH]/2]) // trim bottom
	cube([2Cap[OD2],2Cap[OD2],Cap[LENGTH]],center=true);

	translate([0,0,Cap[LENGTH] + 0.8*Cap[OD1]]) // trim top (arbitrarily)
	cube([2Cap[OD1],2Cap[OD1],2*Cap[OD1]],center=true);

	translate([0,0,-Protrusion])
	cylinder(d=Cord[OD1],h=(Cap[LENGTH] + 2*Protrusion),$fn=NumSides);

	translate([0,0,-Protrusion])
	cylinder(d1=Cord[OD2],d2=Cord[OD1],h=(Cord[LENGTH] + Protrusion),$fn=NumSides);
	}

	}

	if (Layout == "BaseEndCap") {

	Base = [25.2,9.0,12.2]; // base outside dimensions
	Edge = 8.0; // size of sqare ends
	CornerRadius = 0.75;
	Wall = 3; // wall thickness in threads

	ChordHeight = (Base[1] – Edge) / 2;
	ChordRadius = (pow(ChordHeight,2) + pow(Base[0],2)/4) / (2*ChordHeight);

	NumSides = 4*4;

	echo(str("Chord height: ",ChordHeight," radius: ",ChordRadius));

	difference() {
	linear_extrude(height=Base[2],convexity=2) {
	hull() {
	for (i=[-1,1], j=[-1,1])
	translate([i(Base[0]/2 – CornerRadius + WallThreadWidth),j(Base[1]/2 – CornerRadius + WallThreadWidth)])
	circle(r=CornerRadius,$fn=4*4,center=true);
	for (j=[-1,1])
	translate([0,j(ChordHeight + Base[1]/2 – CornerRadius + WallThreadWidth)])
	rotate(180/(2*4))
	circle(r=CornerRadius,$fn=2*4,center=true);
	}
	}

	translate([0,0,3*ThreadThick])
	linear_extrude(height=Base[2],convexity=2)
	intersection() {
	intersection_for (j=[-1,1])
	translate([0,j*(ChordHeight + Base[1]/2 – ChordRadius)])
	circle(r=ChordRadius,$fn=32*4,center=true);
	square([Base[0],2*Base[1]],center=true);
	}
	}
	}

view raw Miniblind cord cap.scad hosted with ❤ by GitHub

The original doodle with some dimensions that didn’t withstand careful measurements:

2016-09-23